1. Field of the Invention
The present invention relates to a pressure sensor, and more particularly, to the structure of a pressure sensor which has a housing, in which a pressure detecting element is stored, and a connector case and is improved in airtightness.
2. Description of the Related Art
There have been proposed various conventional pressure sensors, such as the one described in Japanese Patent Application Laid-Open No. 2002-333377. Here, the pressure sensor disclosed in the patent document is described with reference to FIG. 9. The pressure sensor 101 comprises a housing 110, sensor element 120, holder 130, circuit board 140, spring body 150, connector case 170, and connector 180. In the pressure sensor 101, a pressure sensor body that is formed of the sensor element 120 and the holder 130 is housed in a container that is formed of the housing 110 and the connector case 170.
The housing 110 has a fluid inlet hole 112 through which a fluid is introduced into its lower part. A circular housing base portion 113 is formed on the top part of the inlet hole 112. The housing 110 also has an annular groove 114, a peripheral wall 116 that rises from the outer periphery of the groove 114, a thin-walled crimp portion 117 on the upper end part of the wall 116, and a housing interior space 118 defined by the base portion 113 and the wall 116. The fluid inlet hole 112 and the interior space 118 of the housing 110 communicate with each other.
Further, the sensor element 120 has a function to detect pressure. It is composed of a header 121, a pressure detecting element 122, and a pedestal 123. The detecting element 122 is formed of a semiconductor device in which a plurality of resistors having the piezoelectric resistance effect are formed like a bridge on the top surface of a semiconductor substrate. The pedestal 123 is airtightly fixed on the top surface of the header 121. Sensor element openings 124 that reach the bottom of the detecting element 122 are provided individually in the respective central parts of the header 121 and the pedestal 123.
The semiconductor substrate that forms the pressure detecting element 122 has a rectangular plane shape and is formed with a diaphragm portion. The central part of the diaphragm portion is thinned so that it can be deformed under pressure. A plurality of piezoelectric resistance elements are formed like a bridge on the top surface of the diaphragm portion, whereby a pressure sensing section is formed as a strain gage. Further, electric circuits, such as an amplifier, arithmetic processing circuit, etc., which are manufactured by the IC manufacturing technology, are arranged on a thick-walled portion at the peripheral part.
The holder 130 has a holder opening 132 in the center. The circuit board 140 is fixed on a top surface 134 of the holder 30 with an adhesive or the like. It is in the shape of a disk and has a circuit board opening 141 in its center in which the pressure detecting element 122 of the sensor element 120 is situated.
Furthermore, one end 151 of the spring body 150 is fixed to a lower end part 181 of the connector 180, and its other end side is bent downward and forms a curved portion 153. The connector case 170 is a resin case in which the connector 180 is fixedly inserted. It has a socket portion 171 at its upper part. A first O-ring 195 is inserted in an O-ring receiving groove 114 and prevents water or moisture from externally getting into an interior space 172 of the connector case 170. A second O-ring 196 is fitted on that part of the housing above a thread portion, whereby airtightness between the housing and a pipe is maintained.
According to the prior art described above, the structure at the junction between the pressure sensor body and the connector is simple and requires only a small amount of assembly work, so that the manufacturing cost can be reduced. However, the airtightness should be further improved to maintain the durability and sensitivity of the pressure sensor.